U.S. patent application number 11/385511 was filed with the patent office on 2007-09-27 for system and method for generating radio frequency energy.
This patent application is currently assigned to SHERWOOD SERVICES AG. Invention is credited to James W. McPherson, James H. Orszulak.
Application Number | 20070225698 11/385511 |
Document ID | / |
Family ID | 38198484 |
Filed Date | 2007-09-27 |
United States Patent
Application |
20070225698 |
Kind Code |
A1 |
Orszulak; James H. ; et
al. |
September 27, 2007 |
System and method for generating radio frequency energy
Abstract
An electrosurgical generator is disclosed. The electrosurgical
generator includes a power supply for generating a DC voltage. The
electrosurgical generator also includes a first parallel
inductor-capacitor circuit being driven by a first signal at a
first predetermined frequency and a second parallel
inductor-capacitor inductor-capacitor circuit driven by a second
signal at the first predetermined frequency phase shifted
180.degree.. The electrosurgical generator further includes a
series inductor-capacitor resonant circuit operably connected in
series with a primary winding of a transformer. The first and
second parallel inductor-capacitor circuits are operably connected
to the transformer, such that the first inductor-capacitor circuit
generates a positive half sine wave and the second
inductor-capacitor circuit generates a 180.degree. phase-shifted
positive half sine wave to generate a full sine wave in a secondary
winding of the transformer.
Inventors: |
Orszulak; James H.;
(Nederland, CO) ; McPherson; James W.; (Boulder,
CO) |
Correspondence
Address: |
UNITED STATES SURGICAL,;A DIVISION OF TYCO HEALTHCARE GROUP LP
195 MCDERMOTT ROAD
NORTH HAVEN
CT
06473
US
|
Assignee: |
SHERWOOD SERVICES AG
|
Family ID: |
38198484 |
Appl. No.: |
11/385511 |
Filed: |
March 21, 2006 |
Current U.S.
Class: |
606/34 |
Current CPC
Class: |
A61B 18/1206
20130101 |
Class at
Publication: |
606/034 |
International
Class: |
A61B 18/18 20060101
A61B018/18 |
Claims
1. An electrosurgical generator comprising: a power supply operable
to generate a DC voltage; a first parallel inductor-capacitor
circuit configured to be driven by a first signal at a first
predetermined frequency; a second parallel inductor-capacitor
circuit configured to be driven by a second signal at the first
predetermined frequency phase-shifted 180.degree.; and a series
inductor-capacitor resonant circuit operably connected in series
with a primary winding of a transformer, the first and second
parallel inductor-capacitor circuits operably connected to the
transformer, the first parallel inductor-capacitor circuit being
configured to generate a positive half sine wave from the DC
voltage and the second parallel inductor-capacitor circuit being
configured to generate a 180.degree. phase-shifted positive half
sine wave from the DC voltage to generate a full sine wave in a
secondary winding of the transformer.
2. An electrosurgical generator as in claim 1, wherein the first
parallel inductor-capacitor resonant circuit is tuned to a first
self-resonant frequency that is substantially equivalent to the
first predetermined frequency.
3. An electrosurgical generator as in claim 2, wherein the first
parallel inductor-capacitor resonant circuit includes a first
inductor having a first inductance value and a first capacitor
having a first capacitance value, wherein the first inductance
value and the first capacitance correspond to the first
self-resonant frequency.
4. An electrosurgical generator as in claim 1, wherein the second
parallel inductor-capacitor resonant circuit is tuned to a second
self-resonant frequency that is substantially equivalent to the
first predetermined frequency.
5. An electrosurgical generator as in claim 4, wherein the second
parallel inductor-capacitor resonant circuit includes a second
inductor having a second inductance value and a second capacitor
having a second capacitance value, wherein the second inductance
value and the second capacitance correspond to the second
self-resonant frequency.
6. An electrosurgical generator as in claim 1, wherein the first
and second parallel inductor-capacitor circuit are driven by
switching on and off first and second switching components
respectively.
7. An electrosurgical generator as in claim 6, wherein the first
and second switching components are selected from the group
consisting of transistors, relays, metal-oxide semiconductor
field-effect transistors and insulated gate bipolar
transistors.
8. An electrosurgical generator as in claim 1, wherein the series
inductor-capacitor resonant circuit is tuned to a third
self-resonant frequency that is substantially equivalent to the
predetermined frequency.
9. An electrosurgical generator as in claim 8, wherein the series
inductor-capacitor resonant circuit includes a third inductor
having a third inductance value and a third capacitor having a
third capacitance value, wherein the third inductance value and the
third capacitance correspond to the third self-resonant
frequency.
10. A method for generating high frequency electrosurgical current
comprising the steps of: providing a power supply operable to
generate a DC voltage, a first parallel inductor-capacitor circuit,
a second parallel inductor-capacitor circuit, a series
inductor-capacitor resonant circuit, wherein the first parallel
inductor-capacitor circuit, the second parallel inductor-capacitor
circuit, and the series inductor-capacitor resonant circuit are
operably connected in series with a primary winding of a
transformer; driving the first parallel inductor-capacitor circuit
by a first signal at a first predetermined frequency; driving the
second parallel inductor-capacitor inductor-capacitor circuit by a
second signal at the first predetermined frequency phase-shifted
180.degree.; and generating a positive half sine wave at the first
inductor-capacitor parallel circuit; generating a 180.degree.
phase-shifted positive half sine wave at the second parallel
inductor-capacitor circuit; and combining the positive half sine
wave and the 180.degree. phase-shifted positive half sine wave at a
secondary winding of the transformer to generate a full sine
wave.
11. A method as in claim 10, wherein the first parallel
inductor-capacitor resonant circuit of the providing step is tuned
to a first self-resonant frequency that is substantially equivalent
to the first predetermined frequency.
12. A method as in claim 11, wherein the first parallel
inductor-capacitor resonant circuit of the providing step includes
a first inductor having a first inductance value and a first
capacitor having a first capacitance value, wherein the first
inductance value and the first capacitance correspond to the first
self-resonant frequency.
13. A method as in claim 10, wherein the second parallel
inductor-capacitor resonant circuit of the providing step is tuned
to a second self-resonant frequency that is substantially
equivalent to the first predetermined frequency.
14. A method as in claim 13, wherein the second parallel
inductor-capacitor resonant circuit includes a second inductor
having a second inductance value and a second capacitor having a
second capacitance value, wherein the second inductance value and
the second capacitance correspond to the second self-resonant
frequency.
15. A method as in claim 10, wherein the first and second parallel
inductor-capacitor circuits of the providing step are each driven
in the respective driving steps by switching on and off first and
second switching components respectively.
16. A method as in claim 15, wherein the first and second switching
components are selected from the group consisting of transistors,
relays, metal-oxide semiconductor field-effect transistors and
insulated gate bipolar transistors.
17. A method as in claim 10, wherein the series inductor-capacitor
resonant circuit of the providing step is tuned to a third
self-resonant frequency that is substantially equivalent to the
predetermined frequency.
18. A method as in claim 17, wherein the series inductor-capacitor
resonant circuit of the providing step includes a third inductor
having a third inductance value and a third capacitor having a
third capacitance value, wherein the third inductance value and the
third capacitance correspond to the third self-resonant
frequency.
19. A radio frequency output stage circuit, comprising: a first
parallel inductor-capacitor circuit configured to generate a
positive half sine wave driven by a first signal at a first
predetermined frequency, the first parallel inductor-capacitor
circuit being operably connected to a transformer which includes a
first winding and a series inductor-capacitor resonant circuit
connected in series to a second winding; a second parallel
inductor-capacitor circuit configured to generate a 180.degree.
phase-shifted positive half sine wave driven by a second signal at
the first predetermined frequency phase-shifted 180.degree., the
second parallel inductor-capacitor circuit being operably connected
to the transformer such that the positive half sine wave and the
180.degree. phase-shifted positive half sine wave are combined at
the secondary winding of the transformer to generate a full sine
wave.
Description
BACKGROUND
[0001] 1. Field
[0002] The present disclosure relates generally to electrosurgical
systems and, more specifically, to a system for delivering high
power radiofrequency energy using multiple resonant
inductor-capacitor (LC) networks.
[0003] 2. Description of the Related Art
[0004] Electrosurgery involves application of high radio frequency
(RF) electrical energy to a surgical site to cut, ablate, or
coagulate tissue. In monopolar electrosurgery, a source or active
electrode delivers radio frequency energy from the electrosurgical
generator to the tissue and a return electrode carries the current
back to the generator. In monopolar electrosurgery, the source
electrode is typically part of the surgical instrument held by the
surgeon and applied to the tissue to be treated. A patient return
electrode is placed remotely from the active electrode to carry the
current back to the generator.
[0005] Ablation is a monopolar procedure which is particularly
useful in the field of neurosurgery, where one or more RF ablation
needle electrodes (usually of elongated cylindrical geometry) are
inserted into a living body. A typical form of such needle
electrodes incorporates an insulated sheath from which an exposed
(uninsulated) tip extends. When an RF voltage is provided between
the reference electrode and the inserted ablation electrode, RF
current flows from the needle electrode through the body.
Typically, the current density is very high near the tip of the
needle electrode, which heats and destroys the adjacent tissue.
[0006] In bipolar electrosurgery, one of the electrodes of the
hand-held instrument functions as the active electrode and the
other as the return electrode. The return electrode is placed in
close proximity to the active (current supplying) electrode such
that an electrical circuit is formed between the two electrodes
(e.g., electrosurgical forceps). In this manner, the applied
electrical current is limited to the body tissue positioned between
the electrodes. When the electrodes are sufficiently separated from
one another, the electrical circuit is open and thus inadvertent
contact of body tissue with either of the separated electrodes does
not cause current to flow.
[0007] In electrosurgery, RF energy must be generated having
sufficient frequency, so that the RF energy may be used to cut,
coagulate, etc., tissue by sustaining tissue thermal heating for
prolonged periods of time. Current state of the art electrosurgical
generators do not provide sufficiently powerful RF energy for
prescribed periods of time or they do so in an inefficient manner.
Therefore there is a need for an electrosurgical generator which
can generate high amounts electrosurgical energy in an efficient
manner.
SUMMARY
[0008] The present disclosure provides for an electrosurgical
generator that includes an RF output stage connected to a DC power
supply. The RF output stage includes two connections that receive
DC energy and are connected to a transformer. Each of the two
connections include a switching component that are cycled between
on and off positions at the same frequency but in a 180 degree
out-of-phase relationship and a parallel inductor-capacitor
resonant circuit. The two connections also include a series
inductor-capacitor resonant circuit oriented at a primary winding
of the transformer. The first connection generates a positive
half-sinusoidal waveform and the second connection generates a
180.degree. phase-shifted positive half-sinusoidal waveform. The
waveforms combine at the transformer to form a pure sine output
waveform suitable for electrosurgical procedures involving RF
energy.
[0009] According to one embodiment of the present disclosure, an
electrosurgical generator is disclosed. The electrosurgical
generator includes a power supply for generating a DC voltage. The
electrosurgical generator also includes a first parallel
inductor-capacitor circuit being driven by a first signal at a
first predetermined frequency and a second parallel
inductor-capacitor inductor-capacitor circuit driven by a second
signal at the first predetermined frequency phase shifted
180.degree.. The electrosurgical generator further includes a
series inductor-capacitor resonant circuit operably connected in
series with a primary winding of a transformer. The first and
second parallel inductor-capacitor circuits are operably connected
to the transformer, such that the first inductor-capacitor circuit
generates a positive half sine wave and the second
inductor-capacitor circuit generates a 180.degree. phase-shifted
positive half sine wave to generate a full sine wave in a secondary
winding of the transformer.
[0010] According to another aspect of the present disclosure, a
method for generating high frequency electrosurgical current is
disclosed. The method includes the step of providing a power supply
operable to generate a DC voltage, a first parallel
inductor-capacitor circuit, a second parallel inductor-capacitor
circuit, a series inductor-capacitor resonant circuit. The first
parallel inductor-capacitor circuit, the second parallel
inductor-capacitor circuit, and the series inductor-capacitor
resonant circuit are operably connected in series with a primary
winding of a transformer. The method also includes the steps of
driving a first parallel inductor-capacitor circuit by a first
signal at a first predetermined frequency. The method also includes
the step of driving a second parallel inductor-capacitor
inductor-capacitor circuit by a second signal at the first
predetermined frequency phase-shifted 180.degree.. The method
further includes the steps of generating a positive half sine wave
at the first inductor-capacitor parallel circuit, generating a
180.degree. phase-shifted positive half sine wave at the second
parallel inductor-capacitor circuit, and combining the positive
half sine wave and the 180.degree. phase-shifted positive half sine
wave at the secondary winding of the transformer to generate a full
sine wave.
[0011] According to a further aspect of the present disclosure a
radio frequency (RF) output stage circuit is disclosed. The RF
output stage circuit includes a first parallel inductor-capacitor
circuit configured to generate a positive half sine wave driven by
a first signal at a first predetermined frequency. The first
parallel inductor-capacitor circuit being operably connected to a
transformer which includes a first winding and a series
inductor-capacitor resonant circuit connected in series to a second
winding. The RF output stage circuit also includes a second
parallel inductor-capacitor circuit configured to generate a
180.degree. phase-shifted positive half sine wave driven by a
second signal at the first predetermined frequency phase-shifted
180.degree.. The second parallel inductor-capacitor circuit is
operably connected to the transformer such that the positive half
sine wave and the 180.degree. phase-shifted positive half sine wave
are combined at the secondary winding of the transformer to
generate a full sine wave.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The above and other aspects, features, and advantages of the
present disclosure will become more apparent in light of the
following detailed description when taken in conjunction with the
accompanying drawings in which:
[0013] FIG. 1 is a schematic block diagram of one embodiment of an
electrosurgical system according to the present disclosure;
[0014] FIG. 2 is a schematic block diagram of a generator according
to the present disclosure;
[0015] FIG. 3 is a circuit diagram of a radio frequency (RF) output
stage according to the present disclosure; and
[0016] FIGS. 4A-D are circuit diagrams of alternate embodiments of
the RF output stage according to the present disclosure.
DETAILED DESCRIPTION
[0017] Preferred embodiments of the present disclosure are
described below with reference to the accompanying drawings. In the
following description, well-known functions or constructions are
not described in detail to avoid obscuring the present disclosure
in unnecessary detail. Those skilled in the art will understand
that the invention according to the present disclosure may be
adapted for use with either monopolar, ablation or bipolar
electrosurgical systems.
[0018] FIG. 1 is a schematic illustration of a monopolar
electrosurgical system. The system includes an active electrode 14
and a return electrode 16 for treating tissue of a patient P.
Electrosurgical RF energy is supplied to the active electrode 14 by
a generator 10 via a cable 18 allowing the active electrode 14 to
ablate, cut or coagulate the tissue. The return electrode 16 is
placed at the patient P to return the energy from the patient P to
the generator 10 via a cable 15.
[0019] The generator 10 includes similar input controls (e.g.,
buttons, activators, switches, etc.) for controlling the generator
10. The controls allow the surgeon to adjust power of the RF
energy, waveform, and other parameters to achieve the desired
waveform suitable for a particular task (e.g., cutting,
coagulating, etc.). Disposed between the generator 10 and the
active electrode 14 on the cable 18 is a hand piece 12, which
includes a plurality of input controls that may be redundant with
certain input controls of the generator 10. Placing the input
controls at the hand piece 12 allows for easier and faster
modification of RF energy parameters during the surgical procedure
without returning to the generator 1. Active electrode 14 may
include a temperature sensor, such as a thermocouple, for sensing
temperature at or approximate the surgical site. The temperature
sensor wires may be disposed in cable 18.
[0020] FIG. 2 shows a schematic block diagram of the generator 10
having a microprocessor 22, a high voltage DC power supply 28, and
an RF output stage 30. The microprocessor 22 includes a controller
26 and an output port that is electrically connected to the DC
power supply 28 configured to supply DC power to the RF output
stage 30. The microprocessor 22 receives input signals from the
generator 10 and/or hand piece 12 and the controller 26 in turn
adjusts power outputted by the generator 10, more specifically the
DC power supply 28, and/or performs other control functions
thereon. Furthermore, the generator 10 may include temperature
circuitry 29 for determining the temperature at the surgical site,
which may adjust the power outputted by the generator 10.
[0021] The RF output stage 30 converts DC power into RF energy and
delivers the RF energy to the active electrode 14. In addition, the
RF output stage 30 also receives RF energy from the return
electrode 16. As shown in more detail in FIG. 3, the RF output
stage 30 receives DC voltage from the DC power supply 28 at inputs
40, 42, wherein first and second connections 32, 34 of a first
winding 62 of a transformer 60 create two half-sinusoidal waveforms
180.degree. out-of-phase, which then combine at a secondary winding
64 of the transformer 60 to form a pure (e.g., full) sinusoidal
waveform.
[0022] The power of the DC power supply 28 can be varied to modify
RF magnitude (e.g., amplitude) thereby adjusting the power of the
RF energy delivered to the tissue. This allows for accurate
regulation of the power of delivered RF energy.
[0023] The first and second connections 32, 34 include switching
components 48, 50 and parallel inductor-capacitor resonant circuits
45, 47 (parallel LC circuits 45, 47), respectively. The switching
components 48, 50 may be, for example, transistors, such as
metal-oxide semiconductor field-effect transistors (MOSFET),
insulated gate bipolar transistors (IGBT), and relays. The
switching components 48, 50 are turned on and off at a
predetermined frequency which is also the operating frequency of
the generator 10, thereby closing and opening the first and second
connections 32, 34, respectively. The frequency at which the
switching components 48, 50 are turned on and off is controlled by
a driver (not explicitly shown). The driver emits a
phase-correlated (e.g., the switching components 48, 50 have a
phase relationship) dual drive signal (e.g., .PHI. and
.PHI..sub.--80.degree.). More simply put, the driver signal cycles
the switching components 48, 50 between on and off positions at the
same frequency but out of sync, to create two half-sinusoidal
sinusoidal waveforms 180.degree. out-of-phase. Therefore, adjusting
the phase-correlated dual drive signal provides a means for varying
operating RF frequency. Pulsing of the phase-correlated dual drive
signal also provides means for RF duty cycle control.
[0024] Each of the first and second connections 32, 34 includes the
parallel LC circuits 45, 47, respectively, which convert DC
electrical energy into RF energy, such as AC energy having high
frequency 300 kHz-1000 kHz. The parallel LC circuits 45, 47 include
inductors 44, 46 connected in parallel with first capacitors 52, 54
respectively. When the switching components 48, 50 are closed, DC
power is supplied to the inductors 44, 46, which thereafter
discharge through the first capacitors 52, 54 respectively, when
the switching components 48, 50 are open. This process converts the
constant pulse of DC energy into half-sinusoidal waveforms 70, 72
by the first and second connections 32, 34, respectively. Since the
switching components 48, 50 turn on and off at the same frequency
but 180.degree. out-of-phase, the resulting half-sinusoidal
waveforms 70, 72 are also 180.degree. out-of-phase.
[0025] The first and second connections 32, 34 also include a
series inductor-capacitor (LC) resonant circuit 57 which includes
an inductor 56 and a capacitor 58 oriented on the second connection
34 of the primary winding 62. The series LC circuit 57 and the
parallel LC circuits 45, 47 have a dissimilar resonant operating
frequency. The series LC circuit 57 is preferably within 200 kHz of
the operating frequency, which is 280 kHz. The parallel resonant LC
circuits 45, 47 are preferably within 80 kHz of the operating
frequency which is preferably 544 kHz. The resonant frequency is
based on the inductance and capacitance values of the series LC
circuit 57 and the parallel LC circuits 45, 47 preferably, the
inductance of the inductors 44, 46, 56 and capacitance of the
capacitors 52, 54, 58 are selected which maximize the RF power
developed for performing medical procedures. Inductors 44, 46 may
be 14 .mu.h.gamma. each, the inductor 56 may be 12.5 .mu.h.gamma..
Capacitors 52, 54 may be 0.011 .mu.f and capacitor 58 is 0.0183
.mu.f . The primary winding 62 and inductance contribute to the
series and parallel resonant LC tune and is further optimized
dependent of the RF energy to be delivered by the transformer
60.
[0026] Shown in FIGS. 4A-D are alternate orientations of the
inductor 56 and the capacitor 58. The alternate orientations have
no effect on the functionality of the first and second connections
32, 34. As shown in FIG. 4A, the inductor 56 and the capacitor 58
are oriented on first connection 32, with the capacitor 58 oriented
between the primary winding 62 and the inductor 56. As shown in
FIGS. 4B, the capacitor 58 is oriented on the second connection 34
and the inductor 56 is oriented on the first connection 32. As
shown in FIGS. 4C, the capacitor 58 is oriented on the first
connection 32 and the inductor 56 is oriented on the second
connection 34. FIG. 4D shows the inductor 56 and the capacitor 58
oriented on the second connection 34, with the inductor 56 oriented
between the primary winding 62 and the capacitor 58.
[0027] As discussed above, the switching components 48, 50 are
alternately switched on and off at the same frequency by the phase
correlated dual drive signal. This synchronizes the parallel LC
circuits 45, 47 and the series LC circuit 57 and develops the
half-sinusoidal waveforms 70, 72. The half-sinusoidal waveform 70
is magnetically coupled through the transformer 60 to develop a
positive half-sine voltage to a patient-connective side 68 leading
to the active electrode 14. The half-sinusoidal waveform 72 is
coupled through the transformer 60 to develop a negative half-sine
voltage. The half-sinusoidal waveforms 70, 72 combine on the
secondary winding 64 (e.g., the patient-connective side 68) to
generate a pure sine wave 74 because the half-sinusoidal waveforms
70, 72 are 180.degree. out-of-phase.
[0028] Embodiments of the present disclosure provide for an
electrosurgical generator that includes coupled series and parallel
resonant LC networks. The LC networks permit development of high RF
power without sacrificing high efficiency. More specifically, the
efficiency is due to the reduced power loss of the coupled LC
resonant topology, which minimizes the need for additional heat
removal associated with high power RF energy generation processes.
The dual resonant topology, with combined series and parallel LC
resonant circuit provides efficient energy transfer between
reactive LC components which consume minimal power loss. The only
losses occur as a result of the conductivity losses of the
transistors. There are no switching losses, since the voltage
across the transistors is zero at the time they are activated. By
definition, reactive components the inductors and capacitors in the
LC circuits do not dissipate real power, which allows for high
efficiency. The LC network generates less heat as a result of the
reactive impedance compared to the real power loss associated with
resistive elements. Use of efficient LC resonant energy storage
system also allows for a reduction in weight and form factor for a
given power level.
[0029] In addition, the generator may provide increasing lesion
creation capability, more specifically, the generator allows for
creation of larger ablation volumes in tissue. In particular,
larger lesions require significantly more power (i.e., power
requirements increase exponentially with lesion size). The
generator according to the present disclosure is capable of forming
lesions of diameters 8 cm or larger due to the efficiency of its
power output.
[0030] The described embodiments of the present disclosure are
intended to be illustrative rather than restrictive, and are not
intended to represent every embodiment of the present disclosure.
Various modifications and variations can be made without departing
from the spirit or scope of the disclosure as set forth in the
following claims both literally and in equivalents recognized in
law.
* * * * *